1. Field of the Invention
The present invention relates to a vehicle generator and a generating system that includes the vehicle generator.
2. Description of the Related Art
A vehicle generator has been used for charging battery and supplying electric power to various electric loads such as head lamps.
Such a vehicle generator includes an armature coil, a field coil, a voltage regulator, etc.
The voltage regulator usually employs a duty ratio control circuit that controls field current supplied to the field coil through a switch element. For this purpose, a target output power to be supplied to the electric loads and the battery and a target field current are calculated to provide a suitable duty ratio, which controls the switch element to supply the field coil a suitable amount of field current.
In such a vehicle generator, changes in amount of the field current may be useful for various controls or examinations. For example: disconnection or short-circuiting of the field coil can be detected by comparing the amount of the field current with a preset value; and engine power can be controlled by detecting the amount of the field current because the field current is closely related to the output torque and the rotation speed of the vehicle generator.
However, when the demand of electric power sharply changes in such a case that a heavy electric load is connected or disconnected, the battery may be overcharged, or the electric loads may be oversupplied even if a detected amount of the field current is in a normal level.
JP-A-Hei 2-197299 and JP-A-Sho 56-1736 respectively disclose methods of detecting battery overcharging. However, such an abnormality can not be detected until a considerable time has passed. Even if the abnormality is detected, such a method does not tell whether the abnormality is caused by the field coil or not.